Refrigerator oil and process for lubrication using the refrigerator oil

ABSTRACT

A refrigerator oil, particularly a refrigerator oil for a hydrofluorocarbon refrigerant, comprising a base oil composed of an oxygen-containing organic compound, such as a polyalkylene glycol and polyester, and a fluorinated silicone oil having a kinematic viscosity of 500 mm 2  /sec or more at 25° C. is disclosed. A process for lubrication of a refigeration system comprising lubricating a compression-type refrigeration system by using the refrigerator oil is also disclosed. 
     By using the refrigerator oil, the foaming phenomenon during boiling of the refrigerant dissolved in the refrigerator oil can effectively be suppressed. In the refrigeration system using the refrigerator oil, effective lubrication can be achieved.

TECHNICAL FIELD

The present invention relates to a refrigerator oil, particularly arefrigerator oil for use in combination with a hydrofluorocarbonrefrigerant, and a process for lubrication of a refrigeration systemusing the refrigerator oil. More particularly, the present inventionrelates to a refrigerator oil which can effectively suppress the foamingphenomenon during boiling of the refrigerant dissolved in therefrigerator oil, and a process for lubrication of a refrigerationsystem using the refrigerator oil to maintain the excellent performanceof a compression-type refrigeration system.

BACKGROUND ART

Compression-type refrigerators are generally constituted with acompressor, a condenser, an expansion valve and an evaporator, and has astructure in which a mixed fluid of a refrigerant and a lubricating oilis circulated in the closed system. Heretofore, in the compression-typerefrigerators, dichlorofluoromethane (R12), chlorodifluoromethane (R22)or the like has mainly been used as the refrigerant, and various typesof mineral oil and synthetic oil have been used as the lubricant.

However, chlorofluorohydrocarbons, such as R12 and R22 described above,are being more rigorously restricted world-wide because they bringenvironmental pollution such as the ozonosphere destruction. By thisreason, hydrogen-containing Flon compounds [a "Flon compound" means achlorofluorocarbon, a hydrofluorocarbon, and a hydrochlorofluorocarbonin general] such as hydrofluorocarbons and hydrochlorofluorocarbons areattracting attention as the novel types of refrigerant. Thehydrogen-containing fluorocarbons, particularly hydrofluorocarbons, suchas 1,1,1,2-tetrafluoroethane (Flon 134a), are preferred as therefrigerant for compression-type refrigerators because they have littlepossibility of causing the ozonosphere destruction and can replace Flon12 with little change in the structure of refrigerators which haveheretofore been used.

However, when the hydrofluorocarbon refrigerant described above is used,an unfavorable phenomenon that foaming takes place to a great extentduring boiling of the refrigerant dissolved in the refrigerator oiloccurs. The foaming phenomenon takes place to a greater extentparticularly when a mixed refrigerant containing two or more types ofhydrofluorocarbon is used. When the foaming phenomenon occurs to a greatextent, a large amount of the refrigerator oil flows into therefrigeration system to cause problems that the refrigerating ability isdecreased and that the sufficient lubrication is not achieved because ofdecrease in the amount of the refrigerator oil at the places requiringlubrication. Particularly when a refrigerator of a recent type equippedwith an inverter is used, the problems are greater because a higherspeed of rotation is required at the start of the operation. Therefore,a refrigerator oil which can prevent the foaming phenomenon is requiredmore for a refrigerator of this type than for refrigerators of previoustypes.

The same phenomenon has also been observed with refrigerants of previoustypes. It has empirically been known that the foaming phenomenon in therefrigerants of previous types can be suppressed by adding aconventional silicone oil. However, it is the current situation that,when a hydrofluorocarbon refrigerant is used, the addition of aconventional silicone shows such limited effect of suppressing thefoaming phenomenon that no practical effect can be expected.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a refrigerator oil,particularly a refrigerator oil for use in combination with ahydrofluorocarbon refrigerant, which can effectively suppress thefoaming phenomenon during boiling of the refrigerant dissolved in therefrigerator oil.

Another object of the present invention is to provide a process forlubrication of a refrigeration system using the above refrigerator oilto maintain the excellent performance of a compression-typerefrigeration system.

The present inventors studied extensively to achieve the objectsdescribed above. As the result of such studies, it was discovered that,when a fluorinated silicone oil is added to a specific refrigerator oil,the foaming phenomenon during boiling of a refrigerant dissolved in therefrigerator oil can effectively be suppressed. It was also discoveredthat, in a compression-type refrigeration system, the excellentperformance of the refrigeration system can be maintained by lubricatingthe refrigeration system with the refrigerator oil containing thefluorinated silicone oil described above. The present invention has beencompleted on the basis of the discoveries.

Accordingly, the present invention provides a refrigerator oilcomprising a base oil composed of an oxygen-containing organic compoundand a fluorinated silicone oil having a kinematic viscosity of 500 mm²/sec or more at 25° C. The present invention also provides a process forlubrication of a refrigeration system comprising lubricating acompression-type refrigeration system by using the refrigerator oildescribed above.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

In the present invention, the fluorinated silicone oil contained in therefrigerator oil has a kinematic viscosity of 500 mm² /sec or more at25° C. For example, a fluorinated silicone oil having the structurerepresented by the general formula (I): ##STR1## is preferably used.

In the general formula (I), R¹ to R⁶ represent each hydrogen atom, ahydrocarbon group, or a fluorinated hydrocarbon group, and may be thesame with each other or different from each other. R⁷ and R⁸ representeach a hydrocarbon group or a fluorinated hydrocarbon group, and atleast one of R⁷ and R⁸ is a fluorinated hydrocarbon. Examples of thehydrocarbon group represented by R¹ to R⁸ include alkyl groups having 1to 20 carbon atoms, cycloalkyl groups having 5 to 20 carbon atoms, arylgroups having 6 to 20 carbon atoms, and aralkyl groups having 7 to 20carbon atoms. Examples of the fluorinated hydrocarbon group includefluorinated alkyl groups having 1 to 20 carbon atoms, fluorinatedcycloalkyl groups having 5 to 20 carbon atoms, fluorinated aryl groupshaving 6 to 20 carbon atoms, and fluorinated aralkyl groups having 7 to20 carbon atoms. Particularly, alkyl groups having 1 to 20 carbon atomsand fluorinated alkyl groups having 1 to 20 carbon atoms are preferableas the hydrocarbon group and the fluorinated hydrocarbon group,respectively, because the solubility in the refrigerator oil is low andthe effect of suppressing the foaming phenomenon is great.

R⁷ and R⁸ in a plurality of repeating units may be the same with eachother or different from each other. n represents an integer which isselected in such a manner that the fluorinated silicon oil has akinematic viscosity of 500 mm² /sec or more at 25° C.

The alkyl group having 1 to 20 carbon atoms described above may belinear or branched. Specific examples of the alkyl group having 1 to 20carbon atoms include methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butylgroup, various types of pentyl group, various types of hexyl group,various types of octyl group, various types of decyl group, and varioustypes of dodecyl group. Examples of the cycloalkyl group having 5 to 20carbon atoms include cyclopentyl group, cyclohexyl group, andmethylcyclohexyl group. Examples of the aryl group having 6 to 20 carbonatoms include phenyl group. tolyl group, xylyl group, and naphthylgroup. Examples of the aralkyl group having 7 to 20 carbon atoms includebenzyl group, phenetyl group, and naphthylmethyl group. Examples of thefluorinated alkyl group having 1 to 20 carbon atoms, the fluorinatedcycloalkyl groups having 5 to 20 carbon atoms, the fluorinated arylgroups having 6 to 20 carbon atoms, and the fluorinated aralkyl grouphaving 7 to 20 carbon atoms include groups obtained by substituting oneor more hydrogen atoms in the alkyl groups, the cycloalkyl groups, thearyl groups, and the aralkyl groups, respectively, described above withfluorine atoms.

When the fluorinated silicone oil represented by the general formula (I)has a kinematic viscosity of less than 500 mm² /sec at 25° C., theeffect of suppressing the foaming phenomenon is insufficient, and thefluorinated silicone oil is not preferable. For exhibiting a sufficienteffect of suppressing the foaming phenomenon, the kinematic viscosity at25° C. is preferably 1,000 mm² /sec or more, more preferably 9,000 mm²/sec or more (n is generally more than 100).

The content of the fluorinated silicone oil is not particularly limited.When a hydrofluorocarbon refrigerant is used as the refrigerant, thecontent is preferably in the range that the compatibility of therefrigerator oil and the refrigerant is not adversely affected. Morespecifically, the content is preferably in the range of 1 to 6,000 ppmby weight, more preferably in the range of 10 to 3,000 ppm by weight.When the content is less than 1 ppm by weight, the effect of suppressingthe foaming phenomenon is sometimes not sufficiently exhibited. When thecontent is more than 6,000 ppm by weight, the refrigerator oiloccasionally becomes cloudy. In view of the effect of suppressing thefoaming phenomenon and the stability, it is preferred that thefluorinated silicone oil is contained in such an amount that the productof the kinematic viscosity (mm² /sec) of the fluorinated silicone oil at25° C. and the content (ppm by weight) of the fluorinated silicone oilin the refrigerator oil is in the range of 50,000 to 3,000,000, morepreferably in the range of 100,000 to 2,000,000. When the product isless than 50,000, the effect of suppressing the foaming phenomenon tendsto become small. When the product is more than 3,000,000, there is thepossibility that the refrigerator oil becomes cloudy.

The refrigerator oil of the present invention is used in combinationwith various types of refrigerant, preferably in combination with ahydrofluorocarbon refrigerant. When a hydrofluorocarbon refrigerant isused as the refrigerant, the base oil of the refrigerator oil is notparticularly limited as long as the base oil has a good compatibilitywith the hydrofluorocarbon refrigerant. Specifically, oxygen-containingorganic compounds are preferable as the base oil because of the goodcompatibility with hydrofluorocarbon refrigerants.

Examples of the oxygen-containing organic compound include (1)polyalkylene glycols, (2) polyesters, (3) polyol esters, (4) polyetherketones, (5) polyvinyl ethers, and (6) carbonate derivatives.

As (1) the polyalkylene glycol described above, for example, a compoundrepresented by the general formula (II):

    R.sup.9 --[(OR.sup.10).sub.m --OR.sup.11 ].sub.k           (II)

(wherein R⁹ represents hydrogen atom, an alkyl group having 1 to 10carbon atoms, an acyl group having 2 to 10 carbon atoms, or an aliphatichydrocarbon group having 1 to 10 carbon atoms and 2 to 6 parts forbonding; R¹⁰ represents an alkylene group having 2 to 4 carbon atoms;R¹¹ represents hydrogen atom, an alkyl group having 1 to 10 carbonatoms, or an acyl group having 2 to 10 carbon atoms; k represents aninteger of 1 to 6; and m represents a number which is selected in such amanner that the average of m×k is 6 to 80) can be used.

In the above general formula (II), the alkyl group represented by R⁹ andR¹¹ may be linear, branched linear, or cyclic. Specific examples of thealkyl group include methyl group, ethyl group, n-propyl group, isopropylgroup, various types of butyl group, various types of pentyl group,various types of hexyl group, various types of heptyl group, varioustypes of octyl group, various types of nonyl group, various types ofdecyl group, cyclopentyl group, and cyclohexyl group. When the number ofcarbon atom in the alkyl group is more than 10, the compatibility withhydrofluorocarbon refrigerants is decreased, and phase separationoccasionally takes place. The preferable number of carbon atom in thealkyl group is 1 to 6.

The alkyl group in the acyl group represented by R⁹ and R¹¹ may belinear, branched linear, or cyclic. Specific examples of the alkyl groupinclude alkyl groups having 1 to 9 carbon atoms selected from the alkylgroups described as the examples of the alkyl group in the above. Whenthe number of carbon atom in the acyl group is more than 10, thecompatibility with hydrofluorocarbon refrigerants is decreased, andphase separation occasionally takes place. The preferable number ofcarbon atom in the alkyl group is 2 to 6.

When R⁹ and R¹¹ are both alkyl groups or acyl groups, R⁹ and R₁₁ may bethe same or different.

When k is 2 or more, the plurality of Rll in one molecule may be thesame with each other or different from each other.

When R⁹ is an aliphatic hydrocarbon group having 1 to 10 carbon atomsand 2 to 6 parts for bonding, the aliphatic hydrocarbon group may be anopen-chain group or a cyclic group. Examples of the aliphatichydrocarbon group having 2 parts for bonding include ethylene group,propylene group, butylene group, pentylene group, hexylene group,heptylene group, octylene group, nonylene group, decylene group,cyclopentylene group, and cyclohexylene group. Examples of the aliphatichydrocarbon group having 3 to 6 parts for bonding include residue groupsformed by eliminating hydroxyl groups from polyhydric alcohols, such astrimethylpropane, glycerol, pentaerythritol, sorbitol,1,2,3-trihydroxycylohexane, and 1,3,5-trihydroxycyclohexane.

When the number of carbon atom in the aliphatic hydrocarbon group ismore than 10, the compatibility with hydrofluorocarbon refrigerants isdecreased, and phase separation occasionally takes place. The preferablenumber of carbon atom in the alkyl group is 2 to 6.

R¹⁰ in the above general formula (II) represents an alkylene grouphaving 2 to 4 carbon atoms. Examples of the oxyalkylene group as therepeating unit include oxyethylene group, oxypropylene group, andoxybutylene group. A single type of the oxyalkylene group or 2 or moretypes of the oxyalkylene group may be contained in one molecule. It ispreferred that at least the oxypropylene unit is contained in onemolecule. It is particularly preferred that 50% by mol or more of theoxypropylene unit is contained in the oxyalkylene unit.

k in the above general formula (II) represents an integer of 1 to 6which is determined in accordance with the number of the part forbonding in R⁹. For example, when R⁹ represents an alkyl group or an acylgroup, k represents 1. When R⁹ represents an aliphatic hydrocarbon grouphaving 2, 3, 4, 5, or 6 parts for bonding, k represents 2, 3, 4, 5, or6, respectively. m represents a number which is selected in such amanner that the average of m×k is 6 to 80, preferably 10 to 70. When theaverage of m×k is at the outside of the above range, the objects of thepresent invention cannot sufficiently be achieved.

The polyalkylene glycol represented by the general formula (II) includepolyalkylene glycols having hydroxyl groups at the end. When the contentof the hydroxyl group at the end is 50% by mol or less of the total endgroups, the polyalkylene glycol containing the hydroxyl group at the endcan advantageously be used. However, when the content of the hydroxylgroup at the end is more than 50% by mol, the polyalkylene glycol is notpreferable because the polyalkylene glycol becomes more hygroscopic andthe viscosity index is decreased.

As the polyalkylene glycol described above, polyoxypropylene glycoldimethyl ethers represented by the general formula: ##STR2## (wherein xrepresents a number of 6 to 80), polyoxyethylene polyoxypropylene glycoldimethyl ethers represented by the general formula: ##STR3## (wherein aand b represent each a number of 1 or more, and the sum of a and b is 6to 80), polyoxypropylene glycol monobutyl ethers represented by thegeneral formula: ##STR4## wherein x represents a number of 6 to 80), andpolyoxypropylene glycol diacetate, are preferable in view of the economyand the effect.

As the polyalkylene glycol represented by the general formula (II),compounds described in the specification of Japanese Patent ApplicationLaid-Open No. Heisei 2(1990)-305893 in detail can also be used.

As (2) the polyester described above, an aliphatic polyester derivativehaving a constituting unit represented by the general formula (III):##STR5## (wherein R¹² represents an alkylene group having 1 to 10 carbonatoms, and R¹³ represents an alkylene group having 2 to 10 carbon atomsor an oxaalkylene group having 4 to 20 carbon atoms) and a molecularweight of 300 to 2000 can be used.

In the general formula (III), R¹² represents an alkylene group having 1to 10 carbon atoms. Specific examples of the alkylene group includemethylene group, ethylene group, propylene group, ethylmethylene group,1,1-dimethylethylene group, 1,2-dimethylethylene group, n-butylethylenegroup, isobutylethylene group, 1-ethyl-2-methylethylene group,1-ethyl-1-methylethylene group, trimethylene group, tetramethylenegroup, and pentamethylene group. Alkylene groups having 6 or less carbonatoms are preferable. R¹³ represents an alkylene group having 2 to 10carbon atoms or an oxaalkylene group having 4 to 20 carbon atoms.Specific examples of the alkylene group include the groups describedabove as the specific examples of the alkylene group represented by R¹²(except for methylene group). Alkylene groups having 2 to 6 carbon atomsare preferable. Specific examples of the oxaalkylene group include3-oxa-1,5-pentylene group, 3,6-dioxa-1,8-octylene group,3,6,9-trioxa-1,11-undecylene group, 3-oxa-1,4-dimethyl-1,5-pentylenegroup, 3,6-dioxa-1,4,7-trimethyl-1,8-octylene group,3,6,9-trioxa-1,4,7,10-tetramethyl-1,11-undecylene group,3-oxa-1,4-diethyl-1,5-pentylene group,3,6-dioxa-1,4,7-triethyl-1,8-octylene group,3,6,9-trioxa-1,4,7,10-tetraethyl-1,11-undecylene group,3-oxa-1,1,4,4-tetramethyl-1,5-pentylene group,3,6-dioxa-1,1,4,4,7,7-hexamethyl-1,8-octylene group,3,6,9-trioxa-1,1,4,4,7,7,10,10-octamethyl-1,1,1-undecylene group,3-oxa-1,2,4,5-tetramethyl-1,5-pentylene group,3,6-dioxa-1,2,4,5,7,8-hexamethyl-1,8-octylene group,3,6,9-trioxa-1,2,4,5,7,8,10,11-octamethyl-1,1,1-undecylene group,3-oxa-1-methyl-1,5-pentylene group, 3-oxa-1-ethyl-1,5-pentylene group,3-oxa-1,2-dimethyl-1,5-pentylene group,3-oxa-1-methyl-4-ethyl-1,5-pentylene group,4-oxa-2,2,6,6-tetramethyl-1,7-heptylene group, and4,8-dioxa-2,2,6,6,10,10-hexamethyl-1,11-undecylene group. R¹² and R¹³ ina plurality of constituting units may be the same with each other ordifferent from each other.

The aliphatic polyester derivative represented by the above generalformula (III) preferably has a molecular weight (measured by the gelpermeation chromatography (GPC)) of 300 to 2,000. When the molecularweight is less than 300, the kinematic viscosity is smaller than thedesirable range. When the molecular weight is more than 2,000, thealiphatic polyester derivative becomes waxy. Therefore, a molecularweight at the outside of the specified range is not preferable.

As the aliphatic polyester derivative described above, the compoundsdescribed in the specification of International Patent ApplicationLaid-Open No. WO 91/07479 in detail can also be used.

As (3) the polyol ester described above, a carboxylic acid ester of apolyhydric hydroxy compound containing at least 2 hydroxyl groups can beused. For example, a compound represented by the general formula (IV):

    R.sup.14 [OCOR.sup.15 ].sub.e                              (IV)

can be used.

In the above general formula (IV), R¹⁴ represents a hydrocarbon groupwhich may be linear or branched linear, preferably an alkyl group having2 to 10 carbon atoms. R¹⁵ represents hydrogen atom or a hydrocarbongroup having 1 to 22 carbon atoms, preferably an alkyl group having 2 to16 carbon atoms. e represents an integer of 2 to 6 . A plurality of--OCOR¹⁵ may be the same with each other or different from each other.

The polyol ester represented by the general formula (IV) can be obtainedby bringing a polyhydric alcohol represented by the general formula (V):

    R.sup.14 (OH).sub.e                                        (V)

(wherein R¹⁴ and e are the same as those described above) into reactionwith a carboxylic acid represented by the general formula (VI):

    R.sup.15 COOH                                              (VI)

(wherein R¹⁵ is the same as that described above) or a reactivederivative, such as an ester or a halide, of the carboxylic acid.

Examples of the polyhydric alcohol represented by the above generalformula (V) include ethylene glycol, propylene glycol, butylene glycol,neopentyl glycol, trimethylolethane, trimethylolpropane, glycerol,pentaerythritol, dipentaerythritol, and sorbitol. Examples of thecarboxylic acid represented by the above general formula (VI) includepropionic acid, butyric acid, pivalic acid, valeric acid, caproic acid,heptanoic acid, 3-methylhexanoic acid, 2-ethylhexanoic acid, capricacid, decanoic acid, lauric acid, myristic acid, and palmitic acid.

As (4) the polyether ketone described above, for example, a compoundrepresented by the general formula (VII): ##STR6## (wherein Q representsa residue group of an alcohol having a functionality of 1 to 8; R¹⁶represents an alkylene group having 2 to 4 carbon atoms; R¹⁷ representsmethyl group or ethyl group; R¹⁸ and R²⁰ represent each hydrogen atom,an aliphatic, aromatic, or aromatic-aliphatic hydrocarbon group having20 or less carbon atoms, and may be the same or different; R¹⁹represents an aliphatic, aromatic, or aromatic-aliphatic hydrocarbongroup having 20 or less carbon atoms; s and t represent each a number of0 to 30; v represents a number of 1 to 8, w represents a number of 0 to7, and v+w is in the range of 1 to 8; and u represents 0 or 1) can beused.

In the above general formula (VII), Q represents a residue group of analcohol having a functionality of 1 to 8. Examples of the alcohol havingQ as the residue group include monohydric alcohols, such as aliphaticmonohydric alcohols such as methyl alcohol, ethyl alcohol, linear andbranched propyl alcohols, linear and branched butyl alcohols, linear andbranched pentyl alcohols, linear and branched hexyl alcohols, linear andbranched heptyl alcohols, linear and branched octyl alcohols, linear andbranched nonyl alcohols, linear and branched decyl alcohols, linear andbranched undecyl alcohols, linear and branched dodecyl alcohols, linearand branched tridecyl alcohols, linear and branched tetradecyl alcohols,linear and branched pentadecyl alcohols, linear and branched hexadecylalcohols, linear and branched heptadecyl alcohols, linear and branchedoctadecyl alcohols, linear and branched nonadecyl alcohols, and linearand branched eicosyl alcohols, aromatic alcohols such as phenol,methylphenol, nonylphenol, octylphenol, and naphthol, aromatic-aliphaticalcohols such as benzyl alcohol and phenylethyl alcohol, and compoundsobtained by partial etherification of these alcohols; dihydric alcohols,such as linear and branched aliphatic alcohols such as ethylene glycol,propylene glycol, butylene glycol, neopentyl glycol, and tetramethyleneglycol, aromatic alcohols such as catechol, resorcinol, bisphenol A, andbisphenyldiol, and compounds obtained by partial etherification of thesecompounds; trihydric alcohols, such as linear and branched aliphaticalcohols such as glycerol, trimethylolpropane, trimethylolethane,trimethylolbutane, and 1,3,5-pentanetriol, aromatic alcohols such aspyrogallol, methylpyrogallol, and 5-sec-butylpyrogallol, and compoundobtained by partial etherification of these alcohols; and alcoholshaving a functionality of 4 to 8, such as pentaerythritol, diglycerol,sorbitane, triglycerol, sorbitol, dipentaerythritol, tetraglycerol,pentaglycerol, hexaglycerol, tripentaerythritol, and compounds obtainedby partial etherification of these alcohols.

In the above general formula (VII), the alkylene group having 2 to 4carbon atoms which is represented by R¹⁶ may be linear or branched.Specific examples of the alkylene group include ethylene group,propylene group, ethylethylene group, 1,1-dimethylethylene group, and1,2-dimethylethylene group. Examples of the aliphatic, aromatic, oraliphatic-aromatic hydrocarbon group having 20 or less carbon atomswhich is represented by R¹⁸ to R²⁰ include linear alkyl groups, such asmethyl group, ethyl group, propyl group, butyl group, pentyl group,heptyl group, octyl group, nonyl group, decyl group, undecyl group,lauryl group, myristyl group, palmityl group, and stearyl group;branched alkyl groups, such as isopropyl group, isobutyl group, isoamylgroup, 2-ethylhexyl group, isostearyl group, and 2-heptylundecyl group;aryl groups, such as phenyl group and methylphenyl group; and arylalkylgroups, such as benzyl group.

In the general formula (VII), s and t represent each a number of 0 to30. When s or t is more than 30, the contribution of the ether group inthe molecule increases, and the polyether ketone is not preferable withrespect to the compatibility with hydrofluorocarbon refrigerants, theelectric insulating property, and the hygroscopic property. v representsa number of 1 to 8, and w represents a number of 0 to 7. v and w satisfythe relation that v+w is in the range of 1 to 8. These numbers areaverage numbers and not limited to integers. u represents 0 or 1. Aplurality of R¹⁶ in the number represented by s×v may be the same witheach other or different from each other. A plurality of R¹⁷ in thenumber represented by t×v may be the same with each other or differentfrom each other. When v represents 2 or more, pluralities of s, t, u,R¹⁸, and R¹⁹ each in the number represented by v may be the same witheach other or different from each other. When w represents 2 or more, aplurality of R²⁰ in the number represented by w may be the same witheach other or different from each other.

As the process for producing the polyether ketone represented by thegeneral formula (VII), a generally known process can be used. Forexample, a process in which a secondary alkyloxyalcohol is oxidized by ahypochlorite and acetic acid (Japanese Patent Application Laid-Open No.Heisei 4(1992)-126716) or a process in which a secondary alkyloxyalcoholis oxidized by zirconium hydroxide and a ketone (Japanese PatentApplication Laid-Open No. Heisei 3(1991)-167149) can be used.

As (5) the polyvinyl ether described above, for example, a polyvinylether compound having the constituting unit represented by the generalformula (VIII): ##STR7## wherein R²¹, R²², and R²³ represent eachhydrogen atom or hydrocarbon group having 1 to 8 carbon atoms and may bethe same with each other or different from each other; R²⁴ represents adivalent hydrocarbon group having 1 to 10 carbon atoms or a divalenthydrocarbon group having 2 to 20 carbon atoms and an oxygen atom of theether linkage; R²⁵ represents a hydrocarbon group having 1 to 20 carbonatoms; c represents a number for each repeating unit, the average ofwhich in the group is 0 to 10; R²¹ to R²⁵ in a plurality of constitutingunits may the same with each other or different from each other; andwhen a plurality of R²⁴ O is contained, R²⁴ O may be the same ordifferent) can be used.

A polyvinyl ether compound composed of a block or random copolymercontaining the constituting unit represented by the above generalformula (VIII) and a constituting unit represented by the generalformula (IX): ##STR8## (wherein R²⁶ to R²⁹ represent each hydrogen atomor a hydrocarbon group having 1 to 20 carbon atoms and may be the samewith each other or different from each other, and R²⁶ to R²⁹ in aplurality of constituting units may be the same with each other ordifferent from each other) can also be used.

In the above general formula (VIII), R²¹, R²², and R²³ represent eachhydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms,preferably 1 to 4 carbon atoms, and may be the same with each other ordifferent from each other. Specific examples of the hydrocarbon groupinclude alkyl groups, such as methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, sec-butyl group,tert-butyl group, various types of pentyl group, various types of hexylgroup, various types of heptyl group, and various types of octyl group;cycloalkyl groups, such as cyclopentyl group, cyclohexyl group, varioustypes of methylcyclohexyl group, various types of ethylcycohexyl group,and various types of dimethylcyclohexyl group; aryl groups, such asphenyl group, various types of methylphenyl group, various types ofethylphenyl group, and various types of dimethylphenyl group; adarylakyl groups, such as benzyl group, various types of phenylethylgroup and various types of methylbezyl group. As R²¹, R²², and R²³,hydrogen atom is particularly preferable.

In the general formula (VIII), R²⁴ represents a divalent hydrocarbongroup having 1 to 10 carbon atoms, preferably 2 to 10 carbon atoms, or adivalent hydrocarbon group having 2 to 20 carbon atoms and an oxygenatom of the ether linkage. Specific examples of the divalent hydrocarbongroup having 1 to 10 carbon atoms include divalent aliphatic groups,such as methylene group, ethylene group, phenylethylene group,1,2-propylene group, 2-phenyl-1,2-propylene group, 1,3-propylene group,various types of butylene group, various types of pentylene group,various types of hexylene group, various types of heptylene group,various types of octylene group, various types of nonylene group, andvarious types of decylene group; alicyclic groups obtained by forming 2parts for bonding in alicyclic hydrocarbons, such as cyclohexane,methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, andpropylcyclohexane; divalent aromatic hydrocarbon groups, such as varioustypes of phenylene group, various types methylphenylene group, varioustypes of ethylphenylene group, various types of dimethylphenylene group,and various types of naphthylene group; alkylaromatic groups having onemonovalent part for bonding on each of the alkyl group and the aromaticgroup in alkylaromatic hydrocarbons, such as toluene, xylene, andethylbenzene; and alkylaromatic groups having parts for bonding on thealkyl groups in polyalkylaromatic hydrocarbons, such as xylene anddiethylbenzene. Among these compounds, aliphatic groups having 2 to 4carbon atoms are particularly preferable.

Specific examples of the divalent hydrocarbon group having 2 to 20carbon atoms and an oxygen atom of the ether linkage preferably includemethoxymethylene group, methoxyethylene group, methoxymethylethylenegroup, 1,1-bismethoxymethylethylene group, 1,2-bismethoxy-methylethylenegroup, ethoxymethylethylene group, (2-methoxyethoxy)-methylethylenegroup, and (1-methyl-2-methoxy)methylethylene group. In the generalformula (VIII), c represents the number of repeating of R²⁵ O, theaverage of which is a number in the range of 0 to 10, preferably 0 to 5.When a plurality of R²⁴ O is contained, R²⁴ O may be the same with eachother or different from each other.

In the general formula (VIII), R²⁵ represents a hydrocarbon group having1 to 20 carbon atoms, preferably 1 to 10 carbon atom. Specific examplesof the hydrocarbon group include alkyl groups, such as methyl group,ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutylgroup, sec-butyl group, tert-butyl group, various types of pentyl group,various types of hexyl group, various types of heptyl group, varioustypes of octyl group, various types of nonyl group, and various types ofdecyl group; cycloalkyl groups, such as cyclopentyl group, cylohexylgroup, various types of methylcyclohexyl group, various types ofethylcyclohexyl group, various types of propylcyclohexyl group, andvarious types of dimethylcyclohexyl group; aryl groups, such as phenylgroup, various types of methylphenyl group, various types of ethylphenylgroup, various types of dimethylphenyl group, various types ofpropylphenyl group, various types of trimethylphenyl group, varioustypes of butylphenyl group, and various types of naphthyl group; andarylalkyl groups, such as benzyl group, various types of phenylethylgroup, various types of methylbenzyl group, various types ofphenylpropyl group, and various types of phenylbutyl group.

R²¹ to R²⁵ in a plurality of constituting units may be the same witheach other or different from each other.

The polyvinyl ether compound (1) having the constituting unitrepresented by the general formula (VIII) described above preferably hasa carbon/oxygen ratio by mol in the range of 4.2 to 7.0 When thecarbon/oxygen ratio by mol is less than 4.2, the polyvinyl ethercompound is excessively hygroscopic. When the carbon/oxygen ratio by molis more than 7.0, the compatibility with hydrofluorocarbon refrigerantsis sometimes decreased.

In the general formula (IX) described above, R²⁶ to R²⁹ represent eachhydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms and maybe the same with each other or different from each other. Examples ofthe hydrocarbon group having 1 to 20 carbon atoms include the samegroups as those described in the examples of R²⁵ in the general formula(VIII) described above. R²⁶ to R²⁹ in a plurality of constituting unitsmay be the same with each other or different from each other.

The polyvinyl ether compound (2) composed of a block or random copolymercontaining the constituting unit represented by the general formula(VIII) described above and the constituting unit represented by thegeneral formula (IX) described above preferably has a carbon/oxygenratio by mol in the range of 4.2 to 7.0 When the carbon/oxygen ratio bymol is less than 4.2, the polyvinyl ether compound is excessivelyhygroscopic. When the carbon/oxygen ratio by mol is more than 7.0, thecompatibility with hydrofluorocarbon refrigerants is sometimesdecreased.

In the present invention, a mixture of the polyvinyl ether compound (1)described above and the polyvinyl ether compound (2) also describedabove may also be used.

The polyvinyl ether compound (1) and the polyvinyl ether compound (2)used in the present invention can be prepared by polymerization of thecorresponding vinyl ether monomer and copolymerization of thecorresponding hydrocarbon monomer having an olefinic double bond and thecorresponding vinyl ether monomer, respectively.

As the polyvinyl ether compound used in the present invention, thefollowing compounds are preferable. One of the preferable compounds hasone end group represented by the general formula (X) or (XI): ##STR9##(wherein R³⁰, R³¹, and R³² represent each hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms and may be the same with each other ofdifferent from each other; R³⁵, R³⁶, R³⁷, and R³⁸ represent eachhydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms and maybe the same with each other or different from each other; R³³ representsa divalent hydrocarbon group having 1 to 10 carbon atoms or a divalenthydrocarbon group having 2 to 20 carbon atoms and an oxygen atom of theether leakage; R³⁴ represents a hydrocarbon group having 1 to 20 carbonatoms; p represents a number for each repeating unit, the average ofwhich in the group is 0 to 10; and when a plurality of R³³ O iscontained, R³³ O may be the same with each other or different from eachother) and the other end group represented by the general formula (XII)or (XIII): ##STR10## (wherein R³⁹, R⁴⁰, and R⁴¹ represent each hydrogenatom or a hydrocarbon group having 1 to 8 carbon atoms and may be thesame with each other or different from each other; R⁴⁴, R⁴⁵, R⁴⁶, andR⁴⁷ represent each hydrogen atom or a hydrocarbon group having 1 to 20carbon atoms and may be the same with each other or different from eachother; R⁴² represents a divalent hydrocarbon group having 1 to 10 carbonatoms or a divalent hydrocarbon group having 2 to 20 carbon atoms and anoxygen atom of the ether linkage; R⁴³ represents a hydrocarbon grouphaving 1 to 20 carbon atoms; q represents a number for each repeatingunit, the average of which is in the range of 0 to 10; and when aplurality of R⁴² O is contained, R⁴² O may be the same with each otheror different from each other).

Another of the preferable compounds has one end group represented by thegeneral formula (XII) or (XIII) described above and the other end grouprepresented by the general formula (XIV): ##STR11## (wherein R⁴³, R⁴⁹,and R⁵⁰ represent each hydrogen atom or a hydrocarbon group having 1 to8 carbon atoms and may be the same with each other or different fromeach other).

Among the polyvinyl ether compounds described above, the followingcompounds are particularly preferable as the base oil of therefrigerator oil of the present invention.

(1) Compounds in which one end group has the structure represented bythe general formula (X) or (XI), the other end group has the structurerepresented by the general formula (XII) or (XIII), and in the generalformula (VIII), R²¹, R²², and R²³ represent all hydrogen atoms, crepresents a number of 0 to 4, R²⁴ represents a divalent hydrocarbongroup having 2 to 4 carbon atoms, and R²⁵ represents a hydrocarbon grouphaving 1 to 20 carbon atoms.

(2) Compounds having the constituting unit represented by the generalformula (VIII) alone, in which one end group has the structurerepresented by the general formula (X), the other end group has thestructure represented by the general formula (XII), and in the generalformula (VIII), R²¹, R²², and R²³ represent all hydrogen atoms, crepresents a number of 0 to 4, R²⁴ represents a divalent hydrocarbongroup having 2 to 4 carbon atoms, and R²⁵ represents a hydrocarbon grouphaving 1 to 20 carbon atoms.

(3) Compounds in which one end group has the structure represented bythe general formula (X) or (XI), the other end group has the structurerepresented by the general formula (XIV), and in the general formula(VIII), R²¹, R²², and R²³ represent all hydrogen atoms, c represents anumber of 0 to 4, R²⁴ represents a divalent hydrocarbon group having 2to 4 carbon atoms, and R²⁵ represents a hydrocarbon group having 1 to 20carbon atoms.

(4) Compounds having the constituting unit represented by the generalformula (VIII) alone, in which one end group has the structurerepresented by the general formula (X), the other end group has thestructure represented by the general formula (XIII), and in the generalformula (VIII), R²¹, R²², and R²³ represent all hydrogen atoms, crepresents a number of 0 to 4, R²⁴ represents a divalent hydrocarbongroup having 2 to 4 carbon atoms, and R²⁵ represents a hydrocarbon grouphaving 1 to 20 carbon atoms.

In the present invention, a polyvinyl ether compound having theconstituting unit represented by the general formula (VIII) describedabove, one end group represented by the general formula (X), and theother end group represented by the general formula (XV): ##STR12##(wherein R⁵¹, R⁵², and R⁵³ represent each hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms and may be the same with each other ordifferent from each other; R⁵⁴ and R⁵⁶ represent each a divalenthydrocarbon group having 2 to 10 carbon atoms and may be the same ordifferent; R⁵⁵ and R⁵⁷ represent each a hydrocarbon group having 1 to 10carbon atoms; d and y represent each a number for each repeating unit,the average of which in the group is 0 to 10, and may be the same ordifferent; R⁵⁴ O may be the same or different when a plurality of R⁵⁴ Oare contained; and R⁵⁶ O may be the same or different when a pluralityof R⁵⁶ O are contained) can also be used. Furthermore, in the presentinvention, a polyvinyl ether compound composed of a homopolymer or acopolymer of an alkyl vinyl ether having the constituting unitrepresented by the general formula (XVI) or (XVII): ##STR13## (whereinR⁵⁸ represents a hydrocarbon group having 1 to 8 carbon atoms), amolecular weight of 300 to 1,200, and one end group represented by thegeneral formula (XVIII) or (XIX): ##STR14## (wherein R⁵⁹ represents analkyl group having 1 to 3 carbon atoms, and R⁶⁰ represents a hydrocarbongroup having 1 to 8 carbon atoms) can also be used.

As the polyvinyl ether compound, compounds described in thespecifications of Japanese Patent Application Laid-Open No. Heisei6(1994)-128578, Japanese Patent Application No. Heisei 5(1993)-125649(Laid-Open No. Heisei 6(1994)-234814), Japanese Patent Application No.Heisei 5(1993)-125650 (Laid-Open No. Heisei 6(1994)-234815), JapanesePatent Application No. Heisei 5(1993)-303736, Japanese PatentApplication No. Heisei 6(1994)-280371, and Japanese Patent ApplicationNo. Heisei 6(1994)-283349, in detail can also be used.

As (6) the carbonate derivative described above, for example, apolycarbonate represented by the general formula (XX): ##STR15##(wherein R⁶¹ and R⁶³ represent each a hydrocarbon group having 30 orless carbon atoms or a hydrocarbon group having 2 to 30 carbon atoms andan ether linkage and may be the same or different, R⁶² represents analkylene group having 2 to 24 carbon atoms, f represents an integer of 1to 100, and g represents an integer of 1 to 10 ) can be used.

In the above general formula (XX), R⁶¹ and R⁶³ represent each ahydrocarbon group having 30 or less carbon atoms or a hydrocarbon grouphaving 2 to 30 carbon atoms and an ether linkage. Specific examples ofthe hydrocarbon group having 30 or less carbon atoms include aliphatichydrocarbon groups, such as methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butylgroup, pentyl group, isopentyl group, neopentyl group, n-hexyl group,1,3-dimethylbutyl group, 2,3-dimethylbutyl group, isohexyl group,n-heptyl group, isoheptyl group, 3-methylhexyl group, n-octyl group,2-ethylhexyl group, isooctyl group, n-nonyl group, isononyl group,n-decyl group, isodecyl group, n-undecyl group, isoundecyl group,n-dodecyl group, isododecyl group, n-tridecyl group, isotridecyl group,n-tetradecyl group, isotetradecyl group, n-pentadecyl group,isopentadecyl group, n-hexadecyl group, isohexadecyl group, n-heptadecylgroup, isoheptadecyl group, n-octadecyl group, isooctadecyl group,n-nonadecyl group, isononadecyl group, n-eicosyl group, isoeicosylgroup, and 2-(4-methylpentyl) group; alicyclic hydrocarbon groups, suchas cyclohexyl group, 1-cyclohexenyl group, methylcyclohexyl group,dimethylcyclohexyl group, decahydronaphthyl group, and tricyclodecanylgroup; aromatic hydrocarbon groups, such as phenyl group, o-tolyl group,p-tolyl group, m-tolyl group, 2,4-xylyl group, mesityl group, and1-naphthyl group; and aromatic-aliphatic hydrocarbons, such as benzylgroup, methylbenzyl group, β-phenylethyl group (phenethyl group),1-phenylethyl group, 1-methyl-1-phenylethyl group, p-methylbenzyl group,styryl group, and cinnamyl group.

As the hydrocarbon group having 2 to 30 carbon atoms and an etherlinkage, for example, a glycol ether group represented by the generalformula (XXI):

    --(R.sup.64 --O).sub.h --R.sup.65                          (XXI)

(wherein R⁶⁴ represents an alkylene group having 2 or 3 carbon atoms,such as ethylene group, propylene group, and trimethylene group, R⁶⁵represents an aliphatic, alicyclic, or aromatic hydrocarbon group having28 or less carbon atoms, such as the groups described as examples of thegroup represented by R⁶¹ and R⁶³, and h represents an integer of 1 to20) can be used. Specific examples of the glycol ether group representedby the general formula (XXI) include ethylene glycol monomethyl ethergroup, ethylene glycol monobutyl ether group, diethylene glycolmono-n-butyl ether group, triethylene glycol monoethyl ether group,propylene glycol monomethyl ether group, propylene glycol monobutylether group, dipropylene glycol monoethyl ether group, and tripropyleneglycol mono-n-butyl ether group. Among the groups described above, alkylgroups, such as n-butyl group, isobutyl group, isoamyl group, cyclohexylgroup, isoheptyl group, 3-methylhexyl group, 1,3-dimethylbutyl group,hexyl group, octyl group, and 2-ethylhexyl group; and alkylene glycolmonoalkyl ether groups, such as ethylene glycol monomethyl ether group,ethylene glycol monobutyl ether group, diethylene glycol monomethylether group, triethylene glycol monomethyl group, propylene glycolmonomethyl ether group, propylene glycol monobutyl ether group,dipropylene glycol monoethyl ether group, and tripropylene glycolmono-n-butyl ether group; are preferable.

R⁶⁸ and R⁶³ described above may be the same or different.

In the above general formula (XX), R⁶² represents an alkylene grouphaving 2 to 24 carbon atoms. Specific examples of the alkylene groupinclude ethylene group, propylene group, butylene group, amylene group,methylamylene group, ethylamylene group, hexylene group, methylhexylenegroup, ethylhexylene group, octamethylene group, nonamethylene group,decamethylene group, dodecamethylene group, and tetradecamethylenegroup. f represents an integer of 1 to 100, and g represents an integerof 1 to 10 . When a plurality of R⁶² O are contained, R⁶² O may be thesame with each other or different from each other.

The polycarbonate represented by the general formula (XX) preferably hasa molecular weight (a weight-average molecular weight) of 300 to 3,000,more preferably 400 to 1,500. When the molecular weight is less than300, the polycarbonate has a kinematic viscosity smaller than thedesirable range and is not preferable as lubricant. When the molecularweight is more than 3,000, the polycarbonate becomes waxy, and theapplication as lubricant is difficult.

The polycarbonate can be produced in accordance with various processesand is generally produced by using a carbonic acid diester or aderivative which can form a carbonic acid ester such as phosgen, and analiphatic dihydric alcohol as the materials.

For producing the polycarbonate from the above materials, a conventionalprocess for producing a polycarbonate can be used. In general, thetransesterification process or the phosgen process can be used.

As the polycarbonate, the compounds described in the specification ofJapanese Patent Application Laid-Open No. Heisei 3(1991)-217495 indetail can also be used.

As the carbonate derivative, a glycol ether carbonate represented by thegeneral formula (XXII):

    R.sup.66 --O--(R.sup.68 O).sub.i --CO--(OR.sup.69).sub.j --O--R.sup.67(XXII)

(wherein R⁶⁶ and R⁶⁷ represent each an aliphatic, alicyclic, aromatic,or aromatic-aliphatic hydrocarbon group having 1 to 20 carbon atoms andmay be the same with each other or different from each other, R⁶⁸ andR⁶⁹ represent each ethylene group or isopropylene group and may be thesame or different, and i and j represent each a number of 1 to 100) canalso be used.

In the above general formula (XXII), specific examples of the aliphatichydrocarbon group represented by R⁶⁶ and R⁶⁷ include methyl group, ethylgroup, propyl group, isopropyl group, isobutyl group, s-butyl group,t-butyl group, pentyl group, isopentyl group, neopentyl group, n-hexylgroup, isohexyl group, n-heptyl group, isoheptyl group, n-octyl group,isooctyl group, n-nonyl group, isononyl group, n-decyl group, isodecylgroup, n-undecyl group, isoundecyl group, n-dodecyl group, isododecylgroup, n-tridecyl group, isotridecyl group, n-tetradecyl group,isotetradecyl group, n-pentadecyl group, isopentadecyl group,n-hexadecyl group, isohexadecyl group, n-heptadecyl group, isoheptadecylgroup, n-octadecyl group, isooctadecyl group, n-nonyldecyl group,isononyldecyl group, n-eicosyl group, and isoeicosyl group. Specificexamples of the alicyclic hydrocarbon group include cyclohexyl group,1-cyclohexenyl group, methylcyclohexyl group, dimethylcyclohexyl group,decahydronaphthyl group, and tricyclodecanyl group. Specific examples ofthe aromatic hydrocarbon group include phenyl group, o-tolyl group,p-tolyl group, m-tolyl group, 2,4-xylyl group, mesityl group, and1-naphthyl group. Specific examples of the aromatic-aliphatichydrocarbon group include benzyl group, methylbenzyl group, phenylethylgroup, styryl group, and cinnamyl group.

The glycol ether carbonate represented by the above general formula(XXII) can be produced, for example, by transesterification of apolyalkylene glycol monoalkyl ether in the presence of an excess amountof a carbonic acid ester of an alcohol having a relatively low boilingpoint.

As the glycol ether carbonate described above, compounds described inthe specification of Japanese Patent Application Laid-Open No. Heisei3(1991)-149295 in detail can also be used.

As the carbonate derivative, a carbonic acid ester represented by thegeneral formula (XXIII): ##STR16## (wherein R⁷⁰ and R⁷¹ represent eachan alkyl group having 1 to 15 carbon atoms or a residue group of adihydric alcohol having 2 to 12 carbon atoms and may be the same ordifferent, R⁷² represents an alkylene group having 2 to 12 carbon atoms,and r represents an integer of 0 to 30) can also be used.

In the above general formula (XXIII), R⁷⁰ and R⁷¹ represent each analkyl group having 1 to 15 carbon atoms, preferably 2 to 9 carbon atoms,or a residue group of a dihydric alcohol having 2 to 12 carbon atoms,preferably 2 to 9 carbon atoms, R⁷² represents an alkylene group having2 to 12 carbon atoms, preferably 2 to 9 carbon atoms, and r representsan integer of 0 to 30, preferably 1 to 30. A carbonic acid ester whichdoes not satisfy the above condition is not preferable because theproduct obtained by using it is inferior in various properties, such asthe compatibility with hydrofluorocarbon refrigerants. Specific examplesof the alkyl group having 1 to 15 carbon atoms which is represented byR⁷⁰ and R⁷¹ include methyl group, ethyl group, n-propyl group, n-butylgroup, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group,n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group,n-tridecyl group, n-tetradecyl group, n-pentadecyl group, isopropylgroup, isobutyl group, tert-butyl group, isopentyl group, isohexylgroup, isoheptyl group, isooctyl group, isononyl group, isodecyl group,isoundecyl group, isododecyl group, isotridenyl group, isotetradecylgroup, and isopentadecyl group.

Specific examples of the residue group of a dihydric alcohol having 2 to12 carbon atoms include residue groups formed from ethylene glycol,1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol,2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol,1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol,2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and1,12-dodecanediol.

Specific examples of alkylene group having 2 to 12 carbon atoms which isrepresented by R⁷² include alkylene groups having linear structures andbranched structures, such as ethylene group, trimethylene group,propylene group, tetramethylene group, butylene group,2-methyltrimethylene group, pentamethylene group,2,2-dimethyltrimethylene group, hexamethylene group,2-ethyl-2-methyltrimethylene group, heptamethylene group,2-methyl-2-propyltrimethylene group, 2,2-diethyltrimethylene group,octamethylene group, nonamethylene group, decamethylene group,undecamethylene group, and dodecamethylene group.

The molecular weight of the carbonic acid ester described above is notparticularly limited. Carbonic acid esters having a number-averagemolecular weight of 200 to 3,000 is preferably used because of thesuperior property of sealing the compressor. Carbonic acid esters havingthe number-average molecular weight of 300 to 2,000 is more preferablyused.

As the carbonic acid ester described above, compounds described in thespecification of Japanese Patent Application Laid-Open No. Heisei4(1992)-63893 in detail can also be used.

Among the oxygen-containing compounds described above, polyalkyleneglycols, polyol esters, and polyvinyl ethers are particularly preferablebecause of superior compatibility with hydrofluorocarbon refrigerantsand superior effect of suppressing the foaming phenomenon. Theoxygen-containing organic compound may be used singly or as acombination of two or more types.

The refrigerator oil of the present invention can be used forrefrigerators using various types of refrigerant, and preferably forrefrigerators using a hydrofluorocarbon refrigerant. Examples of thehydrofluorocarbon refrigerant include 1,1,1,2-tetrafluoroethane (R134a),1,1,2,2-tetrafluoroethane (R134), 1,1,1-trifluoroethane (R143a),1,1-difluoroethane (R152a), pentafluoroethane (R125), difluoromethane(R32), trifluoromethane (R23), and mixtures of these compounds. When therefrigerator oil of the present invention is applied to a refrigerationsystem using a refrigerant containing 1,1,1,2-tetrafluoroethane alone, amixed refrigerant containing difluoromethane, or a mixed refrigerantcontaining 2-tetrafluoroethane, particularly superior effect ofsuppressing the foaming phenomenon can be exhibited. Specific examplesof the mixed refrigerants include R407c (a mixture of R134a, R125, andR32), R404a (a mixture of R134a, R125, and R143a), R410a (a mixture ofR32 and R125), and a mixture of R32 and R134a.

The refrigerator oil of the present invention can also be used forrefrigerators using a refrigerant other than the hydrofluorocarbonrefrigerants described above. Examples of the refrigerant other than thehydrofluorocarbon refrigerants include ethers having 2 to 8 carbon atoms(preferably, dimethyl ether, diethyl ether, and methyl ethyl ether),ammonia, carbon dioxide, and hydrocarbons having 1 to 8 carbon atomssuch as alkanes and alkenes (preferably hydrocarbons having 3 or 4carbon atoms such as propane and butane). The refrigerant can be used asa mixture of two or more types. For example, a mixture of ahydrofluorocarbon refrigerant and a refrigerant other than thehydrofluorocarbon refrigerants can be used. Two or more types ofrefrigerant other than the hydrofluorocarbon refrigerants can also beselected suitably and used in combination.

To the refrigerator oil of the present invention, various conventionaladditives, such as extreme pressure agents such as phosphoric acidesters and phosphorous acid esters, phenol antioxidants, amineantioxidants, stabilizers such as phenyl glycidyl ether, cyclohexeneoxide, epoxidized soy bean oil, and other epoxy compounds, andinactivating agents for copper such as benzotriazole and derivatives ofbenzotriazole, can suitably be added if necessary.

The present invention also provides a process for lubrication of arefrigeration system in which the lubrication is achieved by using therefrigerator oil containing the fluorinated silicone oil described abovein a compression-type refrigeration system, particularly in acompression type refrigeration system using a hydrofluorocarbonrefrigerant. In accordance with the above process, the foamingphenomenon occurring during boiling of the refrigerant dissolved in therefrigerator oil can be suppressed to prevent flowing out of a largeamount of the refrigerator oil into the system, and the excellentperformance of the refrigeration system can be maintained.

The present invention is described in more detail with reference toexamples. However, the present invention is not limited by the examples.

Example 1 to 30 and Comparative Examples 1 to 18

Into a pressure resistant glass vessel having an inner diameter of 55 mmand a height of 30 cm, a refrigerator oil and a refrigerant shown inTable 1 in an amounts of 75 ml each were placed. While the mixture wasstirred well (1380 rpm) with a propeller at a room temperature under anequilibrium pressure of the refrigerant, the pressure inside of thevessel was rapidly reduced to an atmospheric pressure. The height of thefoam formed by the reduction in the pressure was measured. The resultwas evaluated in accordance with the following criterion.

Criterion for Evaluation of the Result

⊚: The height of foam was 5 cm or less.

∘: The height of foam was more than 5 cm and 10 cm or less.

Δ: The height of foam was more than 10 cm and 20 cm or less.

×: The height of foam was more than 20 cm.

As the base oil, the defoaming agent, and the refrigerant, the followingmaterials were used.

(1) Base Oil

ester oil: a carboxylic acid ester of pentaerythritol (VG32 and VG68)

PVE oil: polyvinyl ether oil (VG68)

PAG oil: a modified polyalkylene glycol oil containing oxypropylenegroup and oxyethylene group in the main chain (VG46)

polycarbonate oil: (VG56)

alkylbenzene oil: (VG56)

PAO oil: poly-α-olefin (VG68)

mineral oil: (VG32)

The mark in the parenthesis in the above base oils shows the grade inaccordance with Japanese Industrial Standard.

(2) Defoaming Agent

A: R¹ to R⁷ : methyl group, R⁸ : fluorinated propyl group kinematicviscosity: 500 mm² /sec (25° C.)

B: R¹ to R⁷ : methyl group, R⁸ : fluorinated propyl group kinematicviscosity: 1,000 mm² /sec (25° C.)

C: R¹ to R⁷ : methyl group, R⁸ : fluorinated propyl group kinematicviscosity: 10,000 mm² /sec (25° C.)

D: R¹ to R⁶ : methyl group, R⁷ and R⁸ : fluorinated propyl groupkinematic viscosity: 1,000 mm² /sec (25° C.)

E: R¹ to R⁵ : methyl group, R⁶ to R⁸ : fluorinated propyl groupkinematic viscosity: 1,000 mm² /sec (25° C.)

F: R¹ to R.sup. 3 and R⁵ to R⁷ : methyl group, R⁴ : fluorinated hexylgroup, R⁸ : fluorinated propyl group, kinematic viscosity: 1,000 mm²/sec (25° C.)

G: R¹ to R⁷ : methyl group, R⁸ : fluorinated propyl group kinematicviscosity: 170 mm² /sec (25° C.)

The above oils are the fluorinated silicone oils represented by thegeneral formula (I).

H: silicone oil (dimethylsiloxane) kinematic viscosity: 10,000 mm² /sec(25° C.)

I: silicone oil (dimethylsiloxane) kinematic viscosity: 100,000 mm² /sec(25° C.)

(3) Refrigerant

R134a: 1,1,1,2-tetrafluoroethane

R407c: a mixture of 1,1,1,2-tetrafluoroethane, pentafluoroethane, anddifluoromethane

R22: chlorodifluoromethane

                  TABLE 1 - 1                                                     ______________________________________                                        refrigerator oil                                                                           defoaming                                                                     agent    type      result                                               type of            (ppm by                                                                             of      of                                    Example                                                                              base oil    type   weight)                                                                             refrigerant                                                                           evaluation                            ______________________________________                                        1      ester oil (VG32)                                                                          B      100   R134a   ⊚                      2      ester oil (VG32)                                                                          D      100   R134a   ⊚                      3      ester oil (VG32)                                                                          E      100   R134a   ⊚                      4      ester oil (VG32)                                                                          F      100   R134a   ⊚                      5      ester oil (VG68)                                                                          A      100   R407c   ⊚                      6      ester oil (VG68)                                                                          B      100   R407c   ⊚                      7      ester oil (VG68)                                                                          C      100   R407c   ⊚                      8      ester oil (VG68)                                                                          D      100   R407c   ⊚                      9      ester oil (VG68)                                                                          E      100   R407c   ⊚                      10     ester oil (VG68)                                                                          F      100   R407c   ⊚                      11     PVE oil (VG68)                                                                            B      100   R134a   ⊚                      12     PVE oil (VG68)                                                                            D      100   R134a   ⊚                      13     PVE oil (VG68)                                                                            E      100   R134a   ⊚                      14     PVE oil (VG68)                                                                            F      100   R134a   ⊚                      15     PVE oil (VG68)                                                                            C      100   R32     ⊚                      16     PVE oil (VG68)                                                                            C      100   R32/R134a                                                                             ⊚                                                      (3/7)                                         ______________________________________                                    

                  TABLE 1 - 2                                                     ______________________________________                                        refrigerator oil                                                                           defoaming                                                                     agent    type      result                                               type of            (ppm by                                                                             of      of                                    Example                                                                              base oil    type   weight)                                                                             refrigerant                                                                           evaluation                            ______________________________________                                        17     PVE oil (VG68)                                                                            A      1000  R407c   ⊚                      18     PVE oil (VG68)                                                                            B      100   R407c   ⊚                      19     PVE oil (VG68)                                                                            C      10    R407c   ⊚                      20     PVE oil (VG68)                                                                            D      100   R407c   ⊚                      21     PVE oil (VG68)                                                                            E      100   R407c   ⊚                      22     PVE oil (VG68)                                                                            F      100   R407c   ⊚                      23     PAG oil (VG46)                                                                            B      100   R134a   ⊚                      24     PAG oil (VG46)                                                                            D      100   R134a   ⊚                      25     PAG oil (VG46)                                                                            E      100   R134a   ⊚                      26     PAG oil (VG46)                                                                            F      100   R134a   ⊚                      27     polycarbonate                                                                             B      100   R134a   ⊚                             oil (VG46)                                                             28     polycarbonate                                                                             D      100   R134a   ⊚                             oil (VG46)                                                             29     polycarbonate                                                                             E      100   R134a   ⊚                             oil (VG46)                                                             30     polycarbonate                                                                             F      100   R134a   ⊚                             oil (VG46)                                                             ______________________________________                                    

                  TABLE 1 - 3                                                     ______________________________________                                        refrigerator oil                                                                            defoaming                                                                     agent    type     result                                        Comparative                                                                           type of            (ppm by                                                                             of     of                                    Example base oil    type   weight)                                                                             refrigerant                                                                          evaluation                            ______________________________________                                        1       PVE oil (VG68)                                                                            H      10    R22    ∘                         2       ester oil (VG68)                                                                          H      10    R22    ∘                         3       PVE oil (VG68)                                                                            --     --    R407c  x                                     4       PVE oil (VG68)                                                                            I      100   R407c  x                                     5       ester oil (VG68)                                                                          --     --    R407c  x                                     6       ester oil (VG68)                                                                          I      100   R407c  x                                     7       PAG oil (VG46)                                                                            I      100   R407c  x                                     8       polycarbonate                                                                             I      100   R407c  x                                             oil (VG56)                                                            9       PVE oil (VG68)                                                                            H      10    R134a  x                                     10      ester oil (VG32)                                                                          H      10    R134a  x                                     11      PVE oil (VG68)                                                                            G      100   R407c  x                                     12      PVE oil (VG68)                                                                            G      10,000                                                                              R407c  x                                     13      alkylbenzene                                                                              B      100   R407c  x                                             oil (VG56)                                                            14      PAO oil (VG68)                                                                            B      100   R407c  x                                     15      PVE oil (VG68)                                                                            A      100   R22    Δ                               16      PVE oil (VG68)                                                                            B      100   R22    Δ                               17      PVE oil (VG68)                                                                            C      100   R22    Δ                               18      mineral oil I      100   R22    ∘                         ______________________________________                                    

INDUSTRIAL APPLICABILITY

The refrigerator oil of the present invention can effectively suppressthe foaming phenomenon during boiling of a refrigerant which isdissolved in the refrigerator oil, and used in combination with varioustypes of refrigerant, particularly refrigerants composed of a singletype of hydrofluorocarbon or mixed refrigerants composed of two or moretypes of hydrofluorocarbon. By using the refrigerator oil of the presentinvention as the lubricant in a compression-type refrigeration system,the excellent performance of the refrigeration system can be maintained.

I claim:
 1. A refrigerator oil comprising a base oil composed of anoxygen-containing organic compound and a fluorinated silicone oil havinga kinematic viscosity of 500 mm² /sec or more at 25° C., wherein theoxygen-containing organic compound is polyalkylene glycol, a polyester,a polyether ketone, a polyvinyl ether, or a carbonate derivative,wherein the fluorinated silicone oil is a compound having the structurerepresented by the general formula (I): ##STR17## wherein R¹ to R⁶represent each hydrogen atom or a hydrocarbon group, and may be the samewith each other or different from each other; R⁷ and R⁸ represent each ahydrocarbon group or a fluorinated hydrocarbon group, at least one of R⁷and R⁸ is a fluorinated hydrocarbon, and R⁷ and R⁸ in a plurality ofrepeating units may be the same with each other or different from eachother; and n represents an integer which is selected in such a mannerthat the fluorinated silicone oil has a kinematic viscosity of 500 mm²/sec or more at 25° C., and wherein the content of the fluorinatedsilicone oil in the refrigerator oil is 1 to 6,000 ppm by weight.
 2. Arefrigerator oil according to claim 1, wherein the product of thekinematic viscosity (mm² /sec) at 25° C. of the fluorinated silicone oiland the content (ppm by weight) of the fluorinated silicone oil in therefrigerator oil is 50,000 to 3,000,000.
 3. A process for lubrication ofa refrigeration system comprising lubricating a compression-typerefrigeration system by using the refrigerator oil described in claim 1.4. A refrigerator oil comprising a base oil composed of anoxygen-containing organic compound and a fluorinated silicone oil havinga kinematic viscosity of 500 mm² /sec or more at 25° C., wherein theoxygen-containing organic compound is a polyester, a polyether ketone, apolyvinyl ether, or a carbonate derivative, wherein the fluorinatedsilicone oil is a compound having the structure represented by thegeneral formula (I): ##STR18## wherein R¹ to R⁶ represent each hydrogenatom or a hydrocarbon group, and may be the same with each other ordifferent from each other; R⁷ and R⁸ represent each a hydrocarbon groupor a fluorinated hydrocarbon group, at least one of R⁷ and R⁸ is afluorinated hydrocarbon, and R⁷ and R⁸ in a plurality of repeating unitsmay be the same with each other or different from each other; and nrepresents an integer which is selected in such a manner that thefluorinated silicone oil has a kinematic viscosity of 500 mm² /sec ormore at 25° C., and wherein the content of the fluorinated silicone oilin the refrigerator oil is 1 to 6,000 ppm by weight.